In electrical circuits, such as electronic or optical components, the operation of these components generates heat due to their consumption of power. Such heat, however, is detrimental to many electrical components such as integrated circuits or optical devices. Accordingly, these components typically require cooling beyond mere air convention or ventilation with a fan, for example. In order to accomplish additional cooling, it is known to use heat sink devices that remove heat through thermal conduction in the heat sink device. Typically, these heat sink devices physically contact with components on a substrate such as a circuit board and are constructed of a thermally conductive material, such as metal (e.g., copper or aluminum). Additionally, heat sink devices typically feature a construction having a plurality of fins allowing air movement over a large surface area of the heat sink in order to remove heat through ventilation or natural air convection.
FIG. 1 illustrates a circuit assembly 100, such as a circuit board configured to connect to a PCI or PCI Express, or AGP bus. In particular, the assembly 100 shown in FIG. 1 is a graphics card that is insertable into a PCI Express or AGP bus slot in order to interface with a computing system. The circuit assembly 100 includes a thermal cooling apparatus 102 that is used to effect cooling of components on a circuit substrate 104. The thermal cooling apparatus 102 includes a heat sink structure 106 and air mover, such as a fan 108 that causes air movement or ventilation over fins 110 of the heat sink structure 106. In this example, the heat sink structure 106 within the thermal cooling apparatus 102 is positioned such that it physically contacts components 112 mounted on the circuit substrate 104. In particular, components, such as processing devices, generate more heat than other components, such as memory devices. In this example, a graphics processor chip 114 is illustrated. In order to effect optimal cooling of the graphics processor chip 114, it is known that heat sink structures, such as heat sink 106, must be engaged with the processor 114 with a particular force per unit area (i.e., pressure). As an example, a graphics processing unit requires around 40 pounds per square inch (psi) pressure of the heat sink structure 106 on the processor 114 in order to achieve optimal heat transfer and, thus, cooling of the processor 114. In contrast, devices such as the memory devices 116 only require a pressure around three (3) pounds per square inch (psi) to effect optimal cooling. If more pressure is exerted on components such as the memory devices 116, excessive stress will cause cracking and degradation of these types of devices 116.
FIG. 2 illustrates the back side of the circuit board 104 of the circuit board assembly 100, which is opposite from the top perspective view shown in FIG. 1. This figure illustrates the use of a spring clip 200 that exerts the requisite pressure of the heat sink structure 106 onto either the processor 114 or memory devices 116. The biasing assembly 200 includes a spring bracket 202 that is attached to the thermal cooling apparatus 102 by a pin 204 passing through the circuit substrate 104 or other suitable device. The spring bracket 202 is rotatable around the pin 204 and the pin passes through the circuit substrate 104 to connect the spring bracket 202 to the thermal cooling apparatus 102. The spring bracket 202 also includes a plurality of apertures 206, each of the apertures 206 having a wide portion 208 and a slot portion 210 in order to introduce biasing or force to cause the heat sink structure 106 to put pressure on the processor 114 or memory devices 116. The wide portions 208 of the spring bracket 202 are configured to engage with a plurality of fixed ends 212 affixed to the circuit board 104. The spring bracket 202 is configured such that, when rotated around the pin 204, the slot portions 210 of the apertures 206 engage the fixed pins 212, and pressure is introduced due to the biasing or spring nature of the spring bracket 202. Thus, the heat sink structure 106 is then pressurably engaged with either the processor 114 or the memory devices 116 in order to effect better thermal management of these devices.
In most constructions of circuit assemblies, components, however, have differing heights relative to the surface of the circuit substrates or PCB boards. As an example of such construction, FIG. 3 illustrates a partial sectional elevation view of the circuit assembly illustrated in FIG. 1. As shown, the thermal cooling apparatus 102 featuring heat sink structure 106 is mounted on top of the circuit substrate 104 over a processor 114 and a memory device 116, as examples. The height of the processor (indicated as H1) is significantly greater than a height H2 of the memory device 116. For example, in a graphics processing board, a graphics processing unit can have a height of around 2 millimeters to 2.7 millimeters, whereas memory devices used in such circuits are around 1.1 millimeters in height. Thus, when using a single biasing structure (e.g., spring 202 pin 204, and posts 212), This difference in height leads to either too little pressure on the processing devices such as processor 114 or too much pressure on components such as memory devices 116. In order to compensate for the height difference and alleviate pressure on memory devices 115, for example, an additional plate 302 is included to compensate for the height difference and also to mitigate or reduce pressure exerted on the memory device 115. This use of a plate 302, however, is nonetheless insufficient to prevent eventual stress on the components. Additionally, known thermal cooling apparatus, such as thermal cooling apparatus 102, exhibit intolerance to transportation, shock and vibration due to a rigid fixation of the thermal management device to the circuit substrate.